It is known that piezoelectric sensors positioned under a mattress are suitable for extracting physiological signals, such as cardiac or respiratory signals during little to no motion, and are also suitable for extracting (gross) body movement when the person lying on top of the mattress is moving.
However, in practice it turns out that a huge dynamic range is required to capture both the physiological signals during little to no motion, which are extremely low amplitude signals and the movement signals during motion, which are extremely large amplitude signals. Therefore sleep signal conditioning devices are typically configured to condition the sensor signals to enable measuring the physiological signals in the presence of large signals.
WO2015/078940 proposes to apply an adjustable attenuation to the sensor signal, such that small and large amplitude sensor signals are measurable. The magnitude attenuation factor is taken into account when determining the biophysical variable.
WO 2013/179189 A1 discloses a cardiac activity and respiratory activity, which are monitored of a person lying on a surface of a supporting system. A first signal is generated by sampling a magnitude of a first physical quantity that is representative of the ballistic effect of cardiac activity in the horizontal direction. A second signal is generated by sampling the magnitude of a second physical quantity. The second physical quantity is representative of a change in a pushing effect of the body on the surface in a vertical direction. The changing pushing effect is due to a combination of the expanding and contracting of the body as a result of respiratory activity and of the ballistic effect of cardiac activity in the vertical direction. The first signal and the second signal are processed to extract information about the ballistic effect of the cardiac activity in both the horizontal direction and the vertical direction, and a fourth signal representative of respiratory activity. The first signal is used for identifying in the second signal a contribution from the ballistic effect of cardiac activity in the vertical direction.
US 2009/0093687 A1 discloses a method of communicating with a physiological sensor. In an embodiment, the method includes supplying power through a first conductor in a first mode to the physiological sensor and communicating with an information element through the first conductor in a second mode. The physiological sensor includes the information element, a power supply configured to receive and store power from the first conductor in the first mode, and sensing circuitry configured to receive power from the first conductor in the first mode. The power supply releases the stored power to the sensing circuitry in the second mode.
US 2016/0007870 A1 provides a method of processing a signal representing a physiological rhythm of a subject, wherein the method comprises the steps of receiving the signal from the subject, filtering the signal with a band pass filter, extracting an analysis window from the filtered signal, performing a plurality of interval length estimation methods on the filtered signal in the analysis window, summing the outputs of the plurality of interval length estimation methods, and determining an interval length from the sum of the outputs of the plurality of interval length estimation methods.
WO 2015/078937 A1 discloses a sleep monitoring device for monitoring sleep states of a human, the sleep monitoring device is configured to receive movement data of the resting human from a movement measurement device, the sleep monitoring device comprises a movement data analyzer configured to compute from the movement data at least: heart beat data and respiration data, and physical activity, a data classifier configure to determine a heart rate regularity valuation of the heart beat data within a time interval, and to determine a respiration regularity valuation of the respiration data within the time interval, a sleep classifier configured to obtain a sleep state for the time interval from at least the respiration regularity valuation and the heart rate regularity valuation.
US 2015/0216475 A1 discloses electrodes and methods to determine physiological states using a wearable device (or carried device) and one or more sensors that can be subject to motion. A method includes receiving a sensor signal including data representing physiological characteristics in a wearable device from a distal end of a limb and a motion sensor signal. The method includes decomposing at a processor the sensor signal to determine physiological signal components. A physiological characteristic signal is generated that includes data representing a physiological characteristic, which can form a basis to determine a physiological state based on, for example, bioimpedance signals originating from the distal end of the limb.